A Comparison of the Performance of Recent Sand Control Completions in the Mokoko Abana Field Offshore Cameroon
Authors: David Mason & Maria Pena, Shell; John Cameron & Colin Jones, Weatherford.
The Mokoko Abana field is situated offshore Cameroon. It is a mature oil field initially developed in the 1980s. The sand is unconsolidated and all wells require sand control from start-up as evidenced by sand production if sand control is not effective. Several different types of sand control have been tried with varying degrees of success. This study is mainly focused on three different completions, all in similar configuration high angle wells in the same sand and reservoir.
The first type of completion studied was pre-packed stand alone screens (PPSAS). These showed excellent initial productivity, but were prone to a rapid decline in performance. The decline is attributed to hole collapse, either liberating fines plugging the screen, or creating a low permeability sand/shale mixture in the annular gap.
Open hole gravel packs (OHGP) were then used to support the borehole and immobilize any failed sand and fines in the annulus. The OHGP had a somewhat lower initial productivity than the PPSAS but has maintained a higher level of productivity over time.
Open hole expandable sand screens (ESS) are the most recent completion option, with the first being installed in Q4 2000. The main reasons for installing ESS were a number of reservoir simulation studies which showed better reservoir recovery with a low skin completion, and hence ESS was selected in order to lower the overall skin.
As of 2005, the successful ESS wells, i.e. with correct weave sizing, show a high productivity that has been maintained over four years. An in-depth analysis of the productivity of the PPSAS, OHGP and ESS was undertaken. The analysis was complicated by variation in fluid and sand properties through the reservoir and masked by the different artificial lift methods used. This made an accurate assessment of the performance of each type difficult to achieve. However, even within the uncertainty in the analysis, the ESS completions have a significantly higher productivity and lower skin than the other two completion options.
Although in some other reservoir intervals in the field, the sand is too fine to be retained by the currently available ESS weave sizes, the analysis shows that the ESS represents a very good completion option in certain parts of this field.